There is a need for a broadband or broad bandwidth, low-profile antenna. The bandwidth of an antenna is typically defined as the difference between the low frequency (flow) and high frequency (fhigh) at which the power output of the antenna is within 3 dB of the maximum power output of the antenna. In a broadband or broad bandwidth antenna, the ratio of fhigh to flow is greater than 3:1. The profile of an antenna that includes a ground plane and one or more radiators that are all located to one side of the ground plane refers to a plot of the shortest distance between each point associated with the radiators and the ground plane. For a broadband antenna to be considered to be low-profile, the maximum distance in the profile must be less than λ/2 at flow.
An example of a broadband, high-profile antenna can be found in currently known synthetic-aperture radars. The antenna in such a radar is a single-beam antenna that is capable of broadband performance, mounted to a moving platform (e.g., an aircraft), and used to obtain high spatial resolution images of a target region. To elaborate, the antenna is used to transmit pulses of radio signals of varying wavelengths within the bandwidth and receive echo waveforms that are coherently detected and subsequently processed to obtain a high spatial resolution image of the target region. Currently, the known single-beam, broadband antennas that are used in such radar systems have a high profile (i.e., greater than λ/2 at flow) that is disadvantageous. For example, a high profile limits the application of the antenna to moving platforms that have the space to accommodate the profile of the antenna. A high profile can also adversely affect the operation of the moving platform with which antenna is associated. For example, if the antenna is associated with an aircraft, the high profile may require that a significant portion of the antenna project beyond the normal “skin” of the aircraft and to an extent that adversely affects the aerodynamics of the aircraft.